Regarding the production of products that are adapted to fit the human body, such as clothing, footwear, orthopedic articles, e.g. orthoses and prostheses, it is often required to detect the three-dimensional shape of this body or body part. Various optical scanning methods are known for this purpose, ranging from complex laser triangulation methods to stripe projection systems. In particular a cost-effective photogrammetrical method is known in which the body part to be digitized is covered with a marked elastic envelope, recorded with one or more 2D-cameras from different recording positions overlapping each other, and a 3D-model of this body part is determined by an automatic photogrammetrical evaluation of these views (Robert Massen: Verfahren und Anordnung zur Erfassung der Raumform von Körpern und Körperteilen, EP 0,760,622).
When products which are intended to be in snug contact with the body, e.g. shoes, gloves, prosthesis stumps and the like are produced, the three-dimensional shape of the product does not directly correspond to the three-dimensional shape of the body part. For example the last required for producing a custom-made shoe is substantially narrower than the corresponding foot, as the shoe produced with the aid of the last must somehow compress and form the foot to some extent, in order to produce a good fit.
This difference between the three-dimensional shape of the last and the three-dimensional shape of the foot cannot yet be calculated analytically today. Similarly complicated conditions also apply to custom-made prosthesis funnels for receiving the limb stump. Thus, these custom-made articles produced with the aid of 3D-scan data of the body part often still require complex repeated finishing operations in order to finally obtain the fitting three-dimensional shape.
On the other hand such fitting products are often already available, e.g. an already worn-in and well fitting shoe, glove, prosthesis part, etc. If the three-dimensional shape of this product were known, the producer would have those 3D-data on hand which are required for producing a product that would fit immediately. Unfortunately there have not been any functioning and cost-effective methods for an optical 3D-detection of the interior space of such often cover-shaped products up to now. Indeed it is known to digitize interior spaces with 3D-endoscopes using methods of stereo technology or stripe projection; these methods, however, are complex and require the object to be digitized and the endoscopic systems to be clamped tight, in order to be able to combine the individual 3D-views into a complete model. This clamping as well as the requirement of having to know in each case the exact 3-dimensional recording position of the endoscopic system in relation to the interior space makes the application of these methods more expensive and significantly more complex and thus puts them beyond the options of a specialized orthopedics dealer or shoe store.
Thus, there is a need for a cost-effective and simple system for detecting the three-dimensional shape of interior spaces of products, especially of such products that are adapted to fit the shape of a body part.